1. Field of the Invention
The present invention relates to an optical scanning apparatus and an image forming apparatus, and more particularly to an optical scanning apparatus for scanning a light beam on a scanning surface and an image forming apparatus for forming an image on a recording medium based on image information.
2. Description of the Related Art
Conventionally, image forming apparatuses for forming multicolor images using the Carlson process include image forming apparatuses such that latent images corresponding to black, yellow, magenta, and cyan image elements are formed on each surface of four photoconductor drums by an optical scanning apparatus and toner images obtained by visualizing these latent images using toner corresponding to each color are superimposed and fixed on paper as a recording medium, thereby forming multicolor images.
In recent years, image forming apparatuses of this type have been frequently used for simplified printing as on-demand printing systems and there has been an increasing demand for improvement of productivity thereof and providing high-quality images. According to one method of improving the productivity, the number of the rotation R (rpm) of a polygon mirror for deflecting a light beam and the speed V (m/s) of a transfer body are increased so as to have a faster printing speed.
In general, a relationship between the speed V of the transfer body and the number of the rotation R of the polygon mirror is represented as the following formula:m≧(60/R·N)×(D/25.4)×V 
where m indicates the number of light beams, N indicates the number of deflected surface of the polygon mirror, and D indicates recording density (dpi).
However, when the number of the rotation of the polygon mirror is increased, the amount of heating from a relevant driving system is increased. Thus, a scanning position is changed with the passage of time as a result of distortion of a housing, for example, so that displacement of resist, a tilt of a scanning line, and the like are generated. Accordingly, color drift is generated.
In view of this, a surface emitting semiconductor laser array in which plural luminous sources for emitting light beams are arranged has been frequently used so as to reduce the number of rotation of the polygon mirror within a range such that the above-mentioned formula is satisfied. In a multi-beam optical scanning apparatus using such a laser array with plural luminous sources, if the amount of light in each luminous source is not correctly adjusted, irregularity of thickness is generated on a printed image. Accordingly, the tint of color is changed especially in a multicolor image and this may cause the degradation of image quality.
In view of this, in order to use such a surface emitting semiconductor laser array as a light source, as disclosed in Patent Documents 1 and 2, an image forming apparatus has been proposed in which a light beam from the light source is split and output of the light beam emitting from each luminous source is set to have the same amount while monitoring the split light beam via a light detecting sensor, thereby preventing the degradation of image quality.
However, when a beam splitting optical system and a light detecting sensor are to be disposed in addition, there is a problem in that the number of members, time required for adjustment, and manufacturing costs thereof are increased.
Patent Document 1: Japanese Patent No. 2908652
Patent Document 2: Japanese Laid-Open Patent Application No. 2002-40350